WAEC Chemistry 2015 Objective — Question 28

Question 28 of 50 from the West African Examinations Council (WAEC) Chemistry 2015 Objective paper, with the correct answer and a full explanation.

The following diagram illustrates the rate curve that was obtained when Mg reacted with excess dilute HCl. The diagram became horizontal at X because

A. the reaction was slowed down
B. all the dilute HCl has reacted
C. all the Mg has reactedCorrect
D. hydrogen gas is produced at a steady rate

Explanation

The curve becomes horizontal (flat) at X because the reaction has stopped - all the magnesium (the limiting reagent, since HCl is in excess) has reacted.

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